Seats of this type are disclosed in Japanese Utility Model Laid-Open Nos. 174462/1986 and 101850/1984.
The former Japanese Utility Model Laid-Open No. 174462/1986 discloses an arrangement in which a space is defined within a lower portion of a seat back, a hip support being accommodated within the space in such a manner as to be movable in the forward direction about its lower portion serving as a fulcrum, and when an occupant assumes a seated position in which his hip is moved forwardly, the hip support is moved forwardly so as to project outwardly from a front surface of the seat back, thereby allowing the occupant's hip to be supported by means of this projecting portion. With this arrangement however, when the occupant feels that the support of his hip is insufficient, it is necessary for him to rise up and seat himself again after moving the hip support forwardly a predetermined distance.
In the latter Japanese Utility Model Laid-Open No. 101830/1984, an arrangement is disclosed in accordance with which a space is defined within a lower portion of a seat back, a hip support being disposed within the space in such a manner as to be pivotable back and forth with an upper portion thereof serving as a fulcrum, and a seat plate is connected to a lower portion of the hip support by means of a hinge in such a manner as to be movable back and forth upon a seat cushion. With this arrangement, the occupant is seated upon the seat cushion by means of the seat plate. Accordingly, when the occupant feels that the support of his hip is insufficient, it is necessary for the occupant to rise up, move the hip support forward by pulling the seat plate in the forward direction, and then be seated again.
Thus, with the above-described two examples of the prior art, a drawback is encountered in that the occupant cannot adjust the position of the hip support while being seated.
If a lower region of the lumbar vertebrae is supported by means of a hip support, there is an advantage in that general lumbagos can be alleviated. In addition, if the sacral vertebrae are supported, there is an advantage in that the occupant is able to maintain a stable posture by receiving a reactionary force which occurs when he depresses a pedal of the automobile.
However, with the above-described two examples of the prior art, since a predetermined region of the occupant at a fixed height along the spinal column is to be encountered in order to obtain support, there is the problem that unless the occupant assumes an unnatural posture by moving vertically with respect to the seat, he cannot arbitrarily select the region to be acted upon between the lower region of the lumbar vertebrae and the sacral vertebrae.